1. Field of the Invention
The present invention relates to antenna switching matrices, and more particularly to an add-on system for an existing antenna switching matrix which improves the deblocking performance.
2. Description of the Prior Art
The use of computer controlled digital switching systems in order to control the switching of signals from multiple antenna sources to a plurality of receiver positions is well known in the art. In quantative terms, such switching matrices are often required to selectively interconnect up to 200 input antenna sources with up to 500-1000 output receiver positions. While such switching matrices are preferably designed to be non-blocking, i.e. any input port to output port connection can be made regardless of the state of the matrix, economic considerations many times militate against this optimum design. For example, considering the foregoing example of matricing 200 input antenna sources with 500 receiver positions, a non-blocking rectangular switch matrix may be designed by connecting each input antenna source to 500 different cross points or on-off switches. As a result, 100,000 cross points or switches are required to implement the design with each switch costing in the neighborhood of $300 so that the system cost would approach 30 million dollars. Various types of multi-level switching matrices have been designed in the past to reduce this cost by minimizing the number of cross points used. Such multi-level switching matrices typically comprise an input level or tier and submatrices have a plurality of input ports for connection to the antenna sources, an output level or tier of submatrices having a plurality of output ports supplying the reciever position and a middle level or tier of submatrices interconnecting the input and output levels, the state or switching configuration of the matrix typically being controlled by digital computer operated in response to user input data. While multi-level switching matrices reduce system cost by reducing the number of cross points, which is generally accomplished by minimizing the number of middle level submatrices, there is sometimes required an economic trade-off and as a result the matrix is not completely non-blocking such that a condition may arise where a desired input port to output port cannot be made.
This blocking problem which is somewhat analagous to telephone switching arrangements, has been addressed in the basic design of prior art telecommunications systems. The addressing of this overflow problem in the telephone switching art usually involves a system which is designed from the ground up in order to take advantage of a rearranging system of inputs or outputs in order to provide a desired communication link between an incoming call and its desired telephone. A particular indication of this type of switching is shown by the U.S. Pat. No. 3,566,041, to Ekberg, which sets up a two-stage cross bar switching network which provides overflow links between the cross bar switches of the first stage of a network. This is accomplished by providing a multiple of connections which may be used when blocking is encountered within the network. That is, when each of a first-stage switch has its overflow multiples directly connected to overflow multiples of a plurality of other first-stage switches then when blocking is encountered in the first stage the connection is set up to an overflow path by connecting the "calling" inlet to one of the overflow switches through the use of the cross bar operation. This results in the overflow multiple of a different first-stage switch, to which the first connected overflow multiple is connected, to itself be connected to a suitable cross bar operation to a second coordinate multiple with access to a wanted outlet. This type of structure requires the setting aside of multiples in a plurality of stages, which of course provides an excess cost in the existance of those multiples and which must be designed into the system at its conception and building stage.
Other solutions to the overflow problem involve the setting aside of separate complete channels. Examples of these types of systems include the U.S. Pat. No. 4,146,749 to Pepping et al which discloses a switching system having a dedicated group of access ports for completing connections and a single spare block network provided with a separate programmable identity capable of functioning in place of any of the primary blocks. The patent to Marchetti et al, U.S. Pat. No. 4,160,130 shows a plurality of switch units which each have included therewith a bypass unit for permitting a selected group or class of subscribers to make use of the system following use of certain malfunctions or failures.
Another type of input rearranging type of device in the telecommunications art is shown by the Wang reference, U.S. Pat. No. 4,038,638, which discloses an input-mixed rearrangable network which addresses the problem of a blocked multi-state switching network which occurs because a network happens to be interconnected in a manner that prevents a affecting the desired interconnection. The switching network can perform the function of changing around the inputs to provide a proper connection. Yet another system which can be used to overcome overflow in the telecommuncations art is the loop-around lines which are used if an idle network connection cannot be found through the normally equiped lines as is shown by the patent to Giesken, U.S. Pat. No. 3,816,668. Likewise, the patent to Morino, U.S. Pat. No. 3,823,270 discloses a trunking arrangement having a separate path to a support primary section if a direct path is not available in order to find an available path from a primary to an available secondary.
Each of these prior art devices fail to solve the problem with regard to existing antenna switching matrices because they are either designed from the ground up, involve extensive and costly modifications or most importantly are designed for telecommunications systems which are distinctly different and face different problems than the antenna matrix switching systems. That is, the plurality of antennas must be capable of switching to one or a plurality of the receivers at the output. On the other hand, the type of telecommunications switching arrangements illustrated by the above prior art deals with switching one incoming line to a single output line.
In summation then, the prior art fails to disclose a simple system which can convert an antenna matrix switching system already in existance to a type of system which alleviates the blocking or overflow problem. While many systems have shown procedures for overcoming overflow problems in telecommunications, these systems would not inherently perform the same function in the antenna switching systems and, most importantly, all of these devices are either part of a system designed from the ground up or they involve costly additions of spare and separate complete channels.
The present invention overcomes the problems of the prior art with regard to already existing antenna switching matrix systems through the use of an inexpensive add-on switching system which substantially alleviates the deblocking or overflow problems.